When a crystal defect of a substrate is evaluated, an etching method is frequently used. In an etching method, a crystal defect is manifested as an etch pit by an etchant, and the etch pit is observed by an optical microscope or an electron microscope. When the substrate is a silicon substrate, examples of the etchant include a Sirtl etchant, a Secco etchant, and a Wright etchant. These etchants include hexavalent chromium which adversely affects the environment.
Therefore, the use of a chromeless etchant not containing chromium is reviewed. For example, in the Japanese Industrial Standards, a chromeless etchant containing hydrogen fluoride, nitric acid, acetic acid, and water is standardized as JIS H 0609. However, in this chromeless etchant, there is a problem in that selectivity in which a crystal defect is etched is low, or the etchant reacts with the substrate to generate a new crystal defect.